Integrated-optic intensity modulators with high ON/OFF extinction ratios are key components for applications in optical communication and signal processing. R.C. Alferness in IEEE Transcations on Microwave Theory and Techniques, 1982, discussed conventional devices such as Mach-Zehnder interferometric modulators, uniform directional couplers, reverse .DELTA..beta. couplers, X-switches, and cutoff moduolators for use as optical intensity modulators. Among such devices, the highest extinction ratio ever achieved (greater than 56 dB) was obtained in an electrooptic cutoff modulator with asymmetric strip electrodes as reported by K. Takizawa in Optics Letters, 1986. Unfortunately, waveguide cutoff modulators usually incur a very large insertion loss and require a very high drive voltage for high-extinction operations, thus making their system applications impractical. For other conventional devices, where the achievable extinction ratio is normaly in the range of 15-30 dB, it is rather difficult to obtain higher extinction ratios since critical disign and fabrication are required.